There are three primary objectives for this contract: (a) To provide a Data Center for the Women and infants Transmission Study (WITS), a four site prospective study of vertical transmission of HIV including the effect of HIV infection on pregnancy outcome, the risk of vertical transmission and the natural history of HIV in children; (b) To provide general support for primary and secondary data analysis for the WITS collaborative study of vertical transmission and for secondary analysis of data collected in other clinical studies supported by the AIDS program; (c) To provide analytical support and computer software and hardware assessment to assist the Biostatistics, Research and Epidemiology Branches of the AIDS program in the design, evaluation and monitoring of data coordination activities. The WITS natural history study will provide much needed information on whether the presence of HIV infection during pregnancy, independent of othe factors, increases the likelihood of an adverse pregnancy outcome. It will also permit a determination of those factors that increase the risk for perinatal transmission of the virus, the natural history of the disease in an infected infant, and the impact of pregnancy on the course of the HIV infection in the mother. The second project component addresses the analysis of WITS data, and the combined and pooled analyses of WITS and other related clinical and natural history data, in order to answer questions concerning heterosexual HIV transmission and manifestation. Finally, it will provide a resource for the Epidemiological and Biostatistics Research Branches of NIAID as they support a rapidly growing and complex program of clinical and community based research.